Thin polished plates such as silicon wafers and the like are a very important part of modern technology. A wafer, for instance, may refer to a thin slice of semiconductor material used in the fabrication of integrated circuits and other devices. Other examples of thin polished plates may include magnetic disc substrates, gauge blocks and the like. While the technique described here refers mainly to wafers, it is to be understood that the technique also is applicable to other types of polished plates as well. The term wafer and the term thin polished plate may be used interchangeably in the present disclosure.
Wafers are typically patterned during the fabrication process. Lithography, for example, is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. The performance of a lithography process may be evaluated at least partially based on the minimum feature size (i.e., critical dimension, or CD) and/or the presence of any defective patterns (i.e., pattern defectivity).
It is noted that critical dimension and pattern defectivity observed in silicon wafers are typically affected by focus errors (i.e., defocus) that may occur during patterning in a lithography process. It is also noted that the geometry of a wafer (i.e., wafer geometry) is a factor that may lead to focus errors during lithography. Therein lies a need for systems and methods to help improve critical dimension and pattern defectivity during semiconductor fabrication by taking wafer geometry into consideration.